Traditional ships have been provided with a propulsion propeller and a separate steering rudder. These propulsion and steering means are then generally attached to the stern of the ship so that the driving force for the ship is exerted by the propulsion propeller and operations, such as turning of the ship, are carried out by the rudder.
Recently the propeller and the rudder have been integrated in one propulsion and steering device, a so-called azimuth propeller device. This azimuth propeller device includes one or several propulsion propellers mounted on a shaft placed in an underwater housing or pod, which is turnable around a substantially vertical axis. By turning the shaft it is possible to direct the propeller flow in any direction, and therefore the azimuth propeller may also function as the steering device of the ship.